Abstract
The effect of applying high electrical stresses to liquid paraffin and transformer with fluorescent compounds in solution was investigated under various experimental conditions to allow the conduction and associated electroluminescence phenonena to be observed. The samples were highly degassed to minimise the possibility of oxygen quenching processes, electroluminescence in the stressed region of the gap being observed particularly in the anode region. The conduction current and electroluminescence signals were recorded during each experiment to allow stress conditioning and breakdown effects to be studied. The cross-correlation between, and the magnitude of, the two signals was observed to increase in the period of electrical stressing following a breakdown, the cross-correlation effect becoming more marked as the number of breakdowns increased. Breakdown of the sample was found to result in the formation of thin wax layers on the electrodes,the latter being accompanied by an increase in the breakdown strength of the gap. The thickness of the anode coating was always greater than that on the cathode, and was found to be in keeping with the total breakdown energy in the sample calculated by reference to the test recording. The electroluminescence signal was strongly current dependent, logarithmic plots extending over five decades yielded approximately linear characteristics. Little or no gap dependence being observed. Ultra-violet absorption and emission spectra were obtained from each of the samples before and after testing. No effects attributable to electrical testing were detected. The spectral data was then used to modify the electroluminescence characteristics in an attempt to compensate for the optical characteristics of the sample. The modified characteristics, thought to represent the electrical excitation processes producing electroluminescence were then used with the electrode coating data to discuss the conduction current characteristics.